In the past, endoscope systems including an endoscope whose insertion unit that is elongated and flexible is inserted into a body cavity in order to observe the inside of the body cavity or to, if necessary, collect or cure a tissue in an intracavitary region have been widely adopted.
When the insertion unit of the endoscope included in the endoscope system is inserted into a body cavity, an intracavitary shape and an inserting direction must be judged from an endoscopic image to be seen. Operators are therefore required to be experienced in inserting the insertion unit. For example, assuming that endoscopic examination is performed on the large intestine, the shape of the large intestine is complex and the lumen thereof is narrow and different from person to person. Moreover, when the insertion unit approaches a bent region (sigmoid colon, hepatic curvature, splenic curvature, or the like), an intestinal wall, or an intestinal fold, it becomes hard to determine an inserting direction. The operators are therefore requested to get highly skilled and experienced in inserting the insertion unit.
Conventional endoscopes require the advanced skill and experience of insertion. An endoscope inserting direction detecting apparatus capable of displaying the direction of a lumen, that is, an endoscope inserting direction has therefore been proposed.
For example, an endoscope inserting direction detecting method has been proposed (refer to, for example, Japanese Patent No. 2680111). Herein, a gradient in a change rate at which a quantity characteristic of an endoscopic image changes is compared with a predefined reference value. Points in the endoscopic image at which the gradients are equal to or larger than a predetermined value are sampled as discontinuous points, whereby an object image is produced. The produced object image is divided into a plurality of domains. Suitability for segments are sampled from the respective domains according to a modified Hough transform method. The sampled suitability for segments are divided into groups on a sensory basis according to a predefined criterion, whereby an optimal suitability for a segment is selected. The information on the optimal segment is regarded as a child node, and the sum of a plurality of child nodes or segments is regarded as a parent node or a stripe segment. Finally, the child node concerning the optimal segment is sequentially selected. Resultant small domains are concatenated as start segments of segments. Based on the pattern of the concatenated segments, suitability for segments located at deeper positions are selected in order to determine an endoscope inserting direction.
Moreover, conventional endoscope inserting direction detecting methods include a method proposed in Japanese Unexamined Patent Application Publication No. 2003-93328. According to the proposed method, M sample pixels are selected from a red component of an endoscopic image. Gradient vectors are calculated in order to determine the direction of a gradient in the brightness levels indicated by the sample pixels. The direction of a lumen is then calculated based on the gradient vectors, and indicated with an arrow mark superposed on the endoscopic image.
According to the endoscope inserting direction detecting method proposed in the Japanese Patent No. 2680111, an endoscopic image of the large intestine from which representatives of edges are sampled is divided into a plurality of domains. A representative of an edge useful in detecting the direction of a lumen is detected from each of the domains according to the modified Hough transform. The detected representatives of the edge are concatenated in order to detect the shape of a fold. Consequently, the direction of the lumen is estimated. The process is complex and hard to be executed in real time.
Moreover, the endoscope inserting direction detecting method proposed in the Japanese Unexamined Patent Application Publication 2003-93328 has a drawback. Namely, a halation is sampled from an endoscopic image of the large intestine, and expressed with thin lines. The shape determined with the thin lines is sampled, and a perpendicular at the midpoint of a segment determined with two sampled points is defined. The direction of a lumen is estimated from a position at which a plurality of resultant perpendiculars at the midpoints of segments is converged. If the perpendiculars are not converged at one point, the position of a lumen cannot be determined.
The present invention attempts to break through the foregoing circumstances. An object of the present invention is to provide an endoscope inserting direction detecting apparatus, an endoscope inserting direction detecting system, and an endoscope inserting direction detecting method capable of reliably detecting the direction of a lumen using a simple configuration.